#include <iostream>
#include <vector>
#define rep(i, l, n) for (int i = (l); i < (n); i++)
using namespace std;
template <class T>
using V = vector<T>;


int main(void) {
	int n;	cin >> n;
	V<int> a(n);
	rep(i, 0, n) {
		cin >> a[i];
	}

	int ans = 0;
	rep(i, 0, 36) {
		int same = true;
		int bit = a[0] & 1;	a[0] >>= 1;
		rep(j, 1, n) {
			if ((a[j] & 1) != bit) {
				same = false;
			}
			a[j] >>= 1;
		}
		if (same == false) {
			ans |= 1 << i;
		}
	}

	cout << ans << endl;
	return 0;
}